PS PhD Exit Seminar - Engineering Improved Plant Rubisco Activase for Enhanced Photosynthetic Efficiency

Image

Abstract -  Rubisco activase (Rca) is the essential molecular chaperone that regulates the activity of Rubisco, the enzyme responsible for the initial step of photosynthetic carbon assimilation and providing the primary source of organic carbon on Earth.

In plants, Rca regulates Rubisco activity by facilitating the removal of sugar phosphate inhibitors. As Rca is a relatively thermolabile enzyme, it becomes increasingly unable to maintain Rubisco activity in leaves under moderate heat stress. As a result, attempts to improve the thermostability of Rca have proven successful in boosting plant photosynthesis and productivity under heat stress. Plant Rca’s however can show functional specificity for their Rubisco substrate, sometimes preventing the suitability of introducing naturally thermotolerant Rca variants directly into crops.

To address this challenge, my PhD has sought to better understand and engineer improved Rca function. My thesis has surveyed the temperature kinetics of Rca across 11 plant species with C3, C4, and CAM photosynthetic physiologies to provide a pilot kinetic map of natural Rca diversity. To extend beyond natural variation, my thesis also developed an in vivo high-throughput E. coli selection platform suited to the directed evolution of plant Rca. This screen was used to identify mutations in tobacco Rca that enhanced catalytic function and altered Rubisco substrate specificity. To bridge the gap between bacterial context and plant application, my thesis also trialled a new chloroplast transformation system in tobacco aimed at validating the translational impact of engineered Rca variants on photosynthetic productivity and growth.

Biography - I began my journey in science with an undergraduate degree in Medical Science at the Australian National University, completed in 2018. I then undertook my Honours project at CSIRO in 2019, where I developed a foundation in synthetic biology through engineering RNA-based gene regulatory element, riboswitches through directed evolution to control gene expression in response to novel signal molecules.

Following my Honours year, I joined the Price Lab at RSB as a Research Assistant where I developed a bioreactor system for the in vivo directed evolution of the identification of the cyanobacteria membrane bicarbonate transporter, SbtA, novel mutations.

For my PhD in the Whitney Lab, my project focused on better understanding how to make Rubisco activase more efficient. I developed a novel selection platform in E. coli to evolve improved Rca variants and complemented this with biochemical studies of natural diversity and the development of plant transformation techniques. My thesis provides new SynBio tools for optimizing and translational testing this key regulatory enzyme of photosynthesis to help meet the challenges of global food security.